Numerous thermal therapy devices that apply external treatments to the body are known in the art. Thermal or contrast therapy devices deliver or remove heat to a given therapy area for an effective amount of time in order to achieve a desired therapeutic result. Contrast therapy devices are used to reduce swelling or to encourage healing after swelling has receded. They are also used to soothe muscle and joint pain through the application of heat and compression therapy. Application of heat or cold may be used to heal and rehabilitate injuries to bone, muscle, ligaments, tendons and skin. Cold therapy may be used to reduce swelling, decrease pain, and promote healing of injured tissue. Heat therapy can be used to relax joint tissue, such as ligaments and tendons, to increase range of motion. Thermal therapy can also be used after surgery to reduce pain and swelling and promote healing.
While applying hot and/or cold to sore body parts as therapeutic treatment is well known, the ability to effectively control the therapy temperature of the particular treatment has been problematic. The potential effectiveness of a hot or cold treatment increases as the level of control for the treatment increases. In particular, the effectiveness depends on the ability to control the temperature. If cold treatments are too cold, they may cause skin and tissue damage. Similarly, if hot treatments are too hot, they may burn or otherwise damage the recipient. Therefore, systems for precisely controlling the temperature of a therapy are desirable.
Prior art devices have been developed to deliver hot or cold fluids for therapeutic purposes. For example, U.S. Pat. No. 6,551,347 discloses a heat exchange splint and control unit with a single fluid reservoir and a mixing valve that receives a single input fluid and selectively diverts a first portion of the input fluid to a heat exchanger, while a second portion is diverted past the heat exchanger. The fluid portions recombine at a Y junction, and the temperature of the combined fluid is determined by the relative amount of fluid diverted to the heat exchanger compared to the amount of fluid bypassing the heat exchanger and flowing straight to the Y junction. The temperature of the combined fluid may be set as low as the heat exchanger permits and may achieve a maximum temperature equal to the ambient temperature of the surrounding environment.
Prior art devices have also been developed to alternately deliver hot and cold fluids for therapeutic purposes. For example, U.S. Pat. No. 6,295,819 discloses a thermoelectric heat pump fluid circuit with a single fluid reservoir and a valve that may be selectively toggled between two positions for delivering either a hot or cold fluid. The position of the valve determines which of two fluid temperatures are output by controlling the direction of fluid flow around a heat pump. When the valve is switched, the temperature of fluid in the system gradually shifts form one of two possible therapy temperatures to the other.
The prior art devices do not provide a means for incrementally controlling the output temperature of the therapy fluid supplied to a compressive heat therapy device. Furthermore, there remains a need for a thermal therapy system which includes a means for achieving linear control of the output temperature of a therapy fluid. Previous efforts to provide thermal therapy have included U.S. Pat. No. 2,531,074 which provides a therapy pad wherein heated or cooled water is alternately injected. U.S. Pat. No. 4,149,529 also teaches delivering hot or cold fluid to a compressive therapy device. U.S. Pat. No. 4,756,299 provides a heating pad with various sized holes on its opposite sides. The two sides offer the therapy recipient two different temperatures at which to uses the product.
Systems that can achieve a desired set temperature and do so rapidly, can further increase the benefit of the applied therapy. This is because such systems can be used to avoid the onset of reflex vasodilatation while still giving the analgesic benefits of vasoconstriction. Cold therapy temperatures as high as 40-50 degrees Fahrenheit may induce vasodilatation as the body attempts to warm the effected area. This is know as the ‘hunting effect.’ In order to avoid the hunting effect, but still gain the analgesic benefits of vasoconstriction, a carefully selected cold therapy temperature must be achieved. Generally, a cold therapy temperature of about 55 degrees Fahrenheit will give the benefits of vasoconstriction while avoiding the hunting effect, however, this temperature can vary according to each individual's physiology.
While the above described therapy pads provide for thermal therapy, they are not effective at providing a convenient mixing valve means for controlling the temperature of the delivered therapy fluid. Previous efforts do not provide for linear control of therapy fluid temperature over the range of achievable temperatures. Known thermal therapy mixing valves are only effective at controlling therapy fluid temperatures at the high and low temperature extremes. There remains a need for a thermal therapy system with a mixing valve assembly capable of providing incremental control of therapy fluid temperature changes giving a linear temperature profile over the full range of therapy temperatures.